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On August 30th, 2017, the United States Food and Drug Administration ushered in a new era for genetics, cancer treatment, and personalized medicine with the first U.S. approval of a gene therapy. A drug composed of a patient’s own genetically modified immune cells was quickly approved for the treatment of a cancer called Acute Lymphoblastic Leukemia (ALL) after clinical trials yielded astoundingly promising results. 83% of ALL patients achieved full remission within 3 months of receiving the gene therapy. (more details to follow).

This exciting announcement has understandably taken the media by storm. In effort avoid repeating what has already been said many many many times this week, this article will go beyond the news alerts. We will discuss how the drug, called Kymriah or CLT019, was able to fly through the FDA approval process. We will also provide a detailed biological explanation of how the gene therapy works, and delve into further promise and peril of the new treatment.

A “Breakthrough Therapy” powers through the FDA

Typically when a pharmaceutical company is seeking FDA approval for a new drug or treatment, the drug must pass through an intricately outlined and heavily monitored research and testing sequence called clinical trials. Pre-clinical research plus three phases of human trials are used to establish a drug delivery mechanism (oral pill, injection, etc.), proper drug dosage, and treatment efficacy (effectiveness) and safety in comparison to standard treatments. FDA approval is granted if the new drug is considered an improvement on standard treatments in terms of safety and efficacy. After FDA approval a drug may then be marketed with FDA regulated labeling and monitoring.

This process can take decades, but exceptions can be made for drugs that show early “clinically significant” improvements over currently available treatments. Kymriah, a gene therapy developed by the University of Pennsylvania and Novartis, a Swiss healthcare company, was absolutely one such exception.

ELIANA was the phase II clinical trial of Kymriah in children and young adults who suffered from B-Cell Precursor Acute Lymphoblastic Leukemia (ALL). B-Cell Precursor ALL is a cancer of the blood in which blood-forming cells in the bone marrow overproduce abnormal B-Cells (a type of white blood cell), crowding out red blood cells and platelets. In ELlANA, Kymriah was administered to patients who had experienced poor outcomes with standard leukemia treatments. Of these patients, 83% achieved complete remission of the cancer within three months of receiving Kymriah.

JULIET, an ongoing sister trial to ELIANA, is studying the effect of Kymriah on Diffuse Large B-Cell Lymphoma (DLBCL) in adults. Lymphoma is another cancer of the blood, similar to Leukemia, that originates in infection-fighting white blood cells that are housed in the lymph nodes. An interim analysis of JULIET shows 53% of patients achieving complete remission after receiving Kymriah.

On August 30th, Kymriah became the first gene therapy to earn FDA approval as a treatment for pediatric ALL before ELIANA even reached phase III trials. The JULIET study for DLBCL is ongoing and accelerated.

This is great! But what IS Kymriah? How is it made? How does it work?

Cancer Immunotherapy

Kymriah is a type of cancer immunotherapy. A cancer immunotherapy is a treatment that aims to teach your body’s own natural defense system (the immune system) how to identify and kill cancer cells (also called tumor cells) just as it would identify and kill bacteria, cells infected by viruses, or other sick cells.

But aren’t cancer cells sick? Why does the immune system need to be taught how to kill them? Actually, the immune system is quite good and finding and killing cancer cells. Throughout your life, your immune system is continually fighting and eliminating new cancer cells as they emerge. However, once in a great great while, a cancer cell will develop a mutation that allows it to evade the immune system and multiply out of control. These cancer cells pose a medical conundrum. They are not identified as problematic cells by the immune system, and any chemical drug administered to kill them (chemotherapy) will kill both cancer cells and healthy cells.

Cancer immunotherapy seeks to treat cancer by training the immune system to identify and kill only the escapee cancer cells.

Ok, but how do we “teach” the immune system to find and kill cancer cells?

The scientists who developed Kymriah were able to teach the immune system to kill cancer in patients with ALL by genetically engineering each patient’s T-Cells to recognize and kill cancerous B-Cells.

Definitions:

T-Cell: a type of white blood that plays an important role in the adaptive immune system. In general, T-Cells are responsible for identifying and killing bacteria, cells infected by viruses, and tumor (cancer) cell, but, as explained, cancer cells are really good at hiding from T-Cells.

B-Cell: another type of white blood cell that plays a role in the immune system. In B-Cell Precursor Acute Lymphoblastic Leukemia (ALL), B-Cells are also the type of cell that “went wrong” and are multiplying unchecked. These cancerous B-Cells crowd out other important types of blood cells such as red blood cells, which deliver oxygen around your body, and platelets, which make your blood clot after an injury.

In Kymriah, T-Cells from individual patients are genetically modified to build receptor proteins called a Chimeric Antigen Receptors (CAR). These CAR proteins, which are attached to the surface of the genetically modified T-Cells, are engineered to bind to specific proteins exposed on the surface of the cancer cells. In the case of the Kymriah, the CAR protein is designed to identify CD19, a protein ubiquitous on the surface of B-Cells. When the T-Cell CAR protein binds to CD19, the T-Cell knows it has found a B-Cell. The T-Cell activates and kills the B-Cell.

These types of immunotherapy that utilize T-Cells genetically modified to express CAR proteins are called a CAR-T treatments. CAR + T-Cell = CAR-T.

How are T-Cells Genetically Modified to make CAR-T?

First scientists extract T-Cells from a patient through a prolonged blood draw during which the white blood cells (including the T-Cells) are filtered out and the rest of the blood is returned to the body. The T-Cells are then genetically modified to build CAR proteins through a process called viral transfection. Viral transfection is a method by which scientists intentionally use a virus to deliver new DNA into a cell’s genome. In the case of CAR-T development, scientists usually use a type of virus called a lentivirus to deliver the new genetic material. In nature lentiviruses, are extremely efficient at inserting their own genetic information into host cells in order to hijack the cells’ machinery to build more viruses. Scientists have harnessed this efficient natural mechanism to deliver genetic information of their own design into cells of their own choosing.

Scientists design a segment of RNA, a nucleic acid molecule similar to DNA, that holds the instructions for building a specific CAR protein – in the case of Kymriah, one that will bind to CD19. The RNA is delivered into the T-Cell by viral transfection using the lentivirus. The lentivirus fuses to the T-Cell and releases its contents. The viral RNA is then reverse transcribed (converted) into DNA, and that DNA is inserted into the T-Cell’s genome with the aid of an integrase enzyme, also delivered by the lentivirus. The now genetically modified T-Cell genome holds the instructions to build a CAR protein.

Kymriah / CAR-T treatment Administration

The following is general outline for the Kymriah / CAR-T creation and administration process.

Leukapheresis – White blood cells are extracted from an ALL patient through a prolonged blood draw. The white blood cells (including the T-Cells) are filtered out and the rest of the blood is returned returned to the body.

Lymphodepleting Chemotherapy – Patients undergo a round of chemotherapy to reduce the number of cancer cells and unmodified T-Cells in the body. This will make it easier for the new, modified T-Cells to proliferate (multiply) and kill the remaining cancer cells.

Cell Infusion – The genetically modified T-Cells are injected back into the patient’s bloodstream. This injection only takes a few minutes, and then the new T-Cells go to work!

Why is Kymriah / CAR-T so effective?

Several factors contribute to Kymriah’s incredible clinical trial results. Here we will explain a couple of the big ones.

First, each Kymriah injection is developed specifically for each individual patient using his/her own T-Cells. Previous treatments for Leukemia have included bone marrow transplants in which a patient’s bone marrow (where T-Cells and B-Cells originate) is killed off with chemotherapy and replaced with bone marrow from a healthy individual. The hope is that the new bone marrow will produce only healthy white blood cells and the cancer will go away. While doctors will try to find a bone marrow donor that is a good match for the cancer patient (same blood type, similar genetic profile), the donated bone marrow is never a perfect match. Because immune system cells are supposed to kill any cells they don’t recognize as belonging to their own body, patients who have bone marrow transplants (or any kind of transplant) have to take immunosuppressive drugs to prevent the new white blood cells from the donated marrow from attacking the patient’s body. This condition is called graft vs. host disease. However, immunosuppressive drugs do not always work well enough,and the bone marrow transplants are frequently rejected.Because Kymriah only uses a patient’s own cells, there is no risk of graft vs. host disease or T-Cell rejection. It is truly a personalized medicine.

Second, the new genetically modified T-Cell will keep multiplying after they are injected into the body. After the patient’s T-Cells are genetically modified, they are allowed to proliferate in the lab until several million are present. After these T-Cells are injected back into the patient, they will bind to CD19 expressing B-Cells and activate. Upon activation, a T-Cell will not only kill the cancerous B-Cell, but will also be triggered to start multiplying. An activated T-Cell will also send out chemical signals to neighboring T-Cells to tell them to start multiplying. It is estimated that each T-Cell from the initial injection can yield 10,000 or more additional T-Cells, all carrying the CAR-T genetic modification. After an initial administration of Kymriah CAR-T, there is no need for a second treatment.

Why is viral transfection used for genetic modification and not CRISPR?

Today it’s hard to talk about genetic modification without talking about CRISPR. CRISPR (usually referring to CRISPR-Cas9) is a revolutionary molecular tool that can be used to precisely cut and modify DNA at a desired location with relative ease and extremely high accuracy. CRISPR is the latest and greatest toy in molecular biologists toolbox (For a detailed explanation of CRISPR, please read our previous article “The Future of Genetic Engineering: CRISPR Explained”). Viral transfection using lentivirus is an older genetic modification technique. It is well understood and effective, but not as predictable and easily manipulated as CRISPR. Scientists cannot choose where in the T-Cell genome the new DNA will be inserted. This can cause troublesome disruptions to other important T-Cell genes. So why exactly did the FDA approve a treatment utilizing lentivirus, a genetic modification mechanism that we know to be error prone, whilst CRISPR revolutionizes molecular genetics with its unprecedented precision?

In short, viruses have been used to artificially insert new genes into cells for much much longer than CRISPR has even existed as a molecular tool. Kymriah went into development using lentivirus in 2012, and CRISPR didn’t make its dramatic debut until 2014. CRISPR was simply not an option. All preliminary research and subsequent clinical trials for Kymriah have utilized cells genetically modified by lentivirus, and therefore it is the lentivirus mediated genetic modification that has received FDA approval. Lentivirus spent more time in the pipeline, and CRISPR’s potential shortcomings are not as well researched and understood.

This does not, however, mean that CRISPR is in any way out of the picture. CRISPR may be new, but its astounding potential as a precision gene editing tool is being enthusiastically pursued. Current studies in mice suggest that CRISPR mediated T-Cell gene modifications increase the potency, predictability, and uniformity of CAR-T cancer treatments in comparison to lentivirus mediated modification. It would not be surprising if CRISPR replaces lentivirus as the preferred mechanism for CAR-T genetic modification in the near future.

Further Promise and Peril

Cytokine Release Syndrome

Kymriah may seem like a miracle drug, and it very well may be, but it does have its drawbacks. Primarily, 49% of patients experience a serious and potentially life threatening side effect called Cytokine Release Syndrome (CRS). When T-Cells bind to an antigen (in this case CD19 on cancerous B-Cells), they activate and release signaling molecules called cytokines that tell the body to launch an inflammatory response to help kill the identified invaders (usually pathogens, but in this case cancerous B-Cells). Cytokine release is an important part of a healthy immune response, but in the case of CAR-T treatment, there are millions of cancerous B-Cells all being attacked simultaneously by the millions of newly introduced genetically modified T-Cells. Cytokines are released by the new T-Cells en masse. The resulting mighty inflammatory response may result in high fevers, severe flu-like symptoms, and neurological effects (tremors, headaches, hallucinations, delirium, etc.). In order to treat CRS, The FDA expanded its approval of another drug called Actemra (Tocilizumab). Actemra is an immunosuppressive drug that was originally developed to treat rheumatoid arthritis, but has also proven effective at suppressing the effects of CRS as both applications utilize Actemra’s ability to block cytokines from inciting an inflammatory response. In clinical trials 69% of patients who experienced CRS had complete resolution of symptoms within two weeks of receiving one or two doses of Actemra. Furthermore, Kymriah will only be administered at specific medical centers with staff trained to properly treat CRS and other serious side effects of the Kymriah CAR-T treatment.

Further applications

Novartis and UPenn’s Kymriah received FDA approval for the treatment of ALL, and this only the tip of the iceberg for CAR-T cancer treatments. Not only are researchers attempting to improve the genetic modification process through the use of CRISPR gene editing techniques, but the applications of CAR-T treatment are being explored and showing promise for a many different cancers. Chronic Lymphocytic Leukemia (CLL), different types of Lymphoma, and a wide variety of solid tumors have shown positive responses to CAR-T treatment in various stages of pre-clinical and clinical trials. CAR-T gene therapy is by no means limited to the treatment of Leukemia. CAR-T may be a gift that just keeps on giving. Keep an eye on this one.

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